Question 1050182
Let {{{ t }}} = time in hrs spent running
{{{ 5 - t }}} = time in hrs spent walking
Let {{{ d }}} = the one-way distance she runs
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Equation for running:
(1) {{{ d = 9t }}}
equation for walking:
(2) {{{ d = 3*( 5 - t ) }}}
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Substitute (1) into (2)
(2) {{{ 9t = 3*( 5 - t ) }}}
(2) {{{ 9t = 15 - 3t }}}
(2) {{{ 12t = 15 }}}
(2) {{{ t = 5/4 }}} hrs
and
{{{ 5 - t = 5 - 5/4 }}}
{{{ 5 - t = 20/4 - 5/4 }}}
{{{ 5 - t = 15/4 }}} hrs
{{{ 15/4 = 3 + 3/4 }}}
She should plan on 3 hrs and 45 min for walking
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check answer:
(1) {{{ d = 9t }}}
(1) {{{ d = 9*(5/4) }}} 
(1) {{{ d = 45/4 }}} mi
and
(2) {{{ d = 3*( 5 - t ) }}}
(2) {{{ d = 3*( 5 - 5/4 ) }}}
(2) {{{ d = 15 - 15/4 }}}
(2) {{{ d = 15 - 3 - 3/4 }}}
(2) {{{ d = 12 - 3/4 }}}
(2) {{{ d = 48/4 - 3/4 }}}
(2) {{{ d = 45/4 }}}
OK